59 research outputs found
Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS – Part 2: Application to the global ozonesonde network
Both balloon-borne electrochemical ozonesondes and MOZAIC (measurements of
ozone, water vapour, carbon monoxide and nitrogen oxides by in-service Airbus
aircraft) provide very valuable data sets for ozone studies in the upper
troposphere/lower stratosphere (UTLS). Although MOZAIC's highly accurate
UV-photometers are regularly inspected and recalibrated annually, recent
analyses cast some doubt on the long-term stability of their ozone analysers.
To investigate this further, we perform a 16 yr comparison (1994–2009) of
UTLS ozone measurements from balloon-borne ozonesondes and MOZAIC. The
analysis uses fully three-dimensional trajectories computed from ERA-Interim
(European Centre for Medium-Range Weather Forecasts Re-analysis) wind fields
to find matches between the two measurement platforms. Although different
sensor types (Brewer-Mast and Electrochemical Concentration Cell ozonesondes)
were used, most of the 28 launch sites considered show considerable
differences of up to 25% compared to MOZAIC in the mid-1990s, followed
by a systematic tendency to smaller differences of around 5–10% in
subsequent years. The reason for the difference before 1998 remains unclear,
but observations from both sondes and MOZAIC require further examination to
be reliable enough for use in robust long-term trend analyses starting before
1998. According to our analysis, ozonesonde measurements at tropopause
altitudes appear to be rather insensitive to changing the type of the
Electrochemical Concentration Cell ozonesonde, provided the cathode sensing
solution strength remains unchanged. Scoresbysund (Greenland) showed
systematically 5% higher readings after changing from Science Pump
Corporation sondes to ENSCI Corporation sondes, while a 1.0% KI cathode
electrolyte was retained
Extreme events in total ozone over Arosa – Part 2: Fingerprints of atmospheric dynamics and chemistry and effects on mean values and long-term changes
In this study the frequency of days with extreme low (termed ELOs) and extreme high (termed EHOs) total ozone values and their influence on mean values and trends are analyzed for the world's longest total ozone record (Arosa, Switzerland). The results show (a) an increase in ELOs and (b) a decrease in EHOs during the last decades and (c) that the overall trend during the 1970s and 1980s in total ozone is strongly dominated by changes in these extreme events. After removing the extremes, the time series shows a strongly reduced trend (reduction by a factor of 2.5 for trend in annual mean). Excursions in the frequency of extreme events reveal "fingerprints" of dynamical factors such as ENSO or NAO, and chemical factors, such as cold Arctic vortex ozone losses, as well as major volcanic eruptions of the 20th century (Gunung Agung, El Chichón, Mt. Pinatubo). Furthermore, atmospheric loading of ozone depleting substances leads to a continuous modification of column ozone in the Northern Hemisphere also with respect to extreme values (partly again in connection with polar vortex contributions). Application of extreme value theory allows the identification of many more such "fingerprints" than conventional time series analysis of annual and seasonal mean values. The analysis shows in particular the strong influence of dynamics, revealing that even moderate ENSO and NAO events have a discernible effect on total ozone. Overall the approach to extremal modelling provides new information on time series properties, variability, trends and the influence of dynamics and chemistry, complementing earlier analyses focusing only on monthly (or annual) mean values
Extreme events in total ozone over Arosa – Part 1: Application of extreme value theory
In this study ideas from extreme value theory are for the first time applied in the field of stratospheric ozone research, because statistical analysis showed that previously used concepts assuming a Gaussian distribution (e.g. fixed deviations from mean values) of total ozone data do not adequately address the structure of the extremes. We show that statistical extreme value methods are appropriate to identify ozone extremes and to describe the tails of the Arosa (Switzerland) total ozone time series. In order to accommodate the seasonal cycle in total ozone, a daily moving threshold was determined and used, with tools from extreme value theory, to analyse the frequency of days with extreme low (termed ELOs) and high (termed EHOs) total ozone at Arosa. The analysis shows that the Generalized Pareto Distribution (GPD) provides an appropriate model for the frequency distribution of total ozone above or below a mathematically well-defined threshold, thus providing a statistical description of ELOs and EHOs. The results show an increase in ELOs and a decrease in EHOs during the last decades. The fitted model represents the tails of the total ozone data set with high accuracy over the entire range (including absolute monthly minima and maxima), and enables a precise computation of the frequency distribution of ozone mini-holes (using constant thresholds). Analyzing the tails instead of a small fraction of days below constant thresholds provides deeper insight into the time series properties. Fingerprints of dynamical (e.g. ENSO, NAO) and chemical features (e.g. strong polar vortex ozone loss), and major volcanic eruptions, can be identified in the observed frequency of extreme events throughout the time series. Overall the new approach to analysis of extremes provides more information on time series properties and variability than previous approaches that use only monthly averages and/or mini-holes and mini-highs
Detecting volcanic sulfur dioxide plumes in the Northern Hemisphere using the Brewer spectrophotometer, other networks, and satellite observations
This paper demonstrates that SO 2 columnar amounts have significantly increased following the five
largest volcanic eruptions of the past decade in the Northern Hemisphere. A strong positive signal was detected
by all the existing networks either ground based (Brewer, EARLINET, AirBase) or from satellites (OMI,
GOME-2). The study particularly examines the adequacy of the existing Brewer network to detect SO 2 plumes
of volcanic origin in comparison to other networks and satellite platforms. The comparison with OMI and 45
GOME-2 SO 2 space-borne retrievals shows statistically significant agreement between the Brewer network data
and the collocated satellite overpasses. It is shown that the Brewer instrument is capable of detecting significant columnar SO 2 increases following large volcanic eruptions, when SO 2 levels rise well above the instrumental
noise of daily observations, estimated to be of the order of 2 DU. A model exercise from the MACC project
shows that the large increases of SO 2 over Europe following the Bárðarbunga eruption in Iceland were not
caused by local sources or ship emissions but are clearly linked to the eruption. We propose that by combining
Brewer data with that from other networks and satellites, a useful tool aided by trajectory analyses and modeling
could be created which can be used to forecast high SO 2 values both at ground level and in air flight corridors
following future eruptions
Methods to homogenize electrochemical concentration cell (ECC) ozonesonde measurements across changes in sensing solution concentration or ozonesonde manufacturer
Ozone plays a significant role in the chemical and radiative
state of the atmosphere. For this reason there are many instruments used to
measure ozone from the ground, from space, and from balloons. Balloon-borne
electrochemical cell ozonesondes provide some of the best measurements of the
ozone profile up to the mid-stratosphere, providing high vertical resolution,
high precision, and a wide geographic distribution. From the mid-1990s to the
late 2000s the consistency of long-term records from balloon-borne
ozonesondes has been compromised by differences in manufacturers, Science
Pump (SP) and ENSCI (EN), and differences in recommended sensor solution
concentrations, 1.0 % potassium iodide (KI) and the one-half dilution:
0.5 %. To investigate these differences, a number of organizations
have independently undertaken comparisons of the various ozonesonde types and
solution concentrations, resulting in 197 ozonesonde comparison profiles. The
goal of this study is to derive transfer functions to allow measurements
outside of standard recommendations, for sensor composition and ozonesonde
type, to be converted to a standard measurement and thus homogenize the data
to the expected accuracy of 5 % (10 %) in the stratosphere (troposphere).
Subsets of these data have been analyzed previously and intermediate transfer
functions derived. Here all the comparison data are analyzed to compare (1)Â differences in sensor solution composition for a single ozonesonde type,
(2)Â differences in ozonesonde type for a single sensor solution composition, and
(3)Â the World Meteorological Organization's (WMO) and manufacturers'
recommendations of 1.0 % KI solution for Science Pump and 0.5 % KI for
ENSCI. From the recommendations it is clear that ENSCI ozonesondes and
1.0 % KI solution result in higher amounts of ozone sensed. The results
indicate that differences in solution composition and in ozonesonde type
display little pressure dependence at pressures  ≥  30 hPa, and thus the
transfer function can be characterized as a simple ratio of the less
sensitive to the more sensitive method. This ratio is 0.96 for both solution
concentration and ozonesonde type. The ratios differ at pressures < 30 hPa such that OZ0. 5%/OZ1. 0 % =  0. 90 + 0. 041 ⋅ log10(p) and OZSciencePump/OZENSCI =  0. 764 + 0. 133 ⋅ log10(p) for p in units of hPa. For the manufacturer-recommended
solution concentrations the dispersion of the ratio (SP-1.0 / EN-0.5 %), while
significant, is generally within 3 % and centered near 1.0, such that no
changes are recommended. For stations which have used multiple ozonesonde
types with solution concentrations different from the WMO's and
manufacturer's recommendations, this work suggests that a reasonably
homogeneous data set can be created if the quantitative relationships
specified above are applied to the non-standard measurements. This result is
illustrated here in an application to the Nairobi data set
Past changes in the vertical distribution of ozone - Part 3: Analysis and interpretation of trends
This is the final version of the article. It first appeared from Copernicus Publications via http://dx.doi.org/10.5194/acp-15-9965-2015Abstract. Trends in the vertical distribution of ozone are reported and compared for a number of new and recently revised data sets. The amount of ozone-depleting compounds in the stratosphere (as measured by equivalent effective stratospheric chlorine – EESC) was maximised in the second half of the 1990s. We examine the periods before and after the peak to see if any change in trend is discernible in the ozone record that might be attributable to a change in the EESC trend, though no attribution is attempted. Prior to 1998, trends in the upper stratosphere (~ 45 km, 4 hPa) are found to be −5 to −10 % per decade at mid-latitudes and closer to −5 % per decade in the tropics. No trends are found in the mid-stratosphere (28 km, 30 hPa). Negative trends are seen in the lower stratosphere at mid-latitudes in both hemispheres and in the deep tropics. However, it is hard to be categorical about the trends in the lower stratosphere for three reasons: (i) there are fewer measurements, (ii) the data quality is poorer, and (iii) the measurements in the 1990s are perturbed by aerosols from the Mt Pinatubo eruption in 1991. These findings are similar to those reported previously even though the measurements for the main satellite and ground-based records have been revised. There is no sign of a continued negative trend in the upper stratosphere since 1998: instead there is a hint of an average positive trend of ~ 2 % per decade in mid-latitudes and ~ 3 % per decade in the tropics. The significance of these upward trends is investigated using different assumptions of the independence of the trend estimates found from different data sets. The averaged upward trends are significant if the trends derived from various data sets are assumed to be independent (as in Pawson et al., 2014) but are generally not significant if the trends are not independent. This occurs because many of the underlying measurement records are used in more than one merged data set. At this point it is not possible to say which assumption is best. Including an estimate of the drift of the overall ozone observing system decreases the significance of the trends. The significance will become clearer as (i) more years are added to the observational record, (ii) further improvements are made to the historic ozone record (e.g. through algorithm development), and (iii) the data merging techniques are refined, particularly through a more rigorous treatment of uncertainties.
The support of SPARC, IO3C, IGACO-O3 and NDACC was essential to the success of
the initiative. Neil Harris thanks the UK Natural Environment Research Council for an Advanced
Research Fellowship. Work at the Jet Propulsion Laboratory was performed under contract
with the National Aeronautics and Space Administration. Measurements at Lauder are core funded through New Zealand’s
Ministry of Business, Innovation and Employment, while those at Woolongong are supported
by the Australian Research Council
Quality assessment of the Ozone_cci Climate Research Data Package (release 2017) – Part 2: Ground-based validation of nadir ozone profile data products
Atmospheric ozone plays a key role in
air quality and the radiation budget of the Earth, both directly and through
its chemical influence on other trace gases. Assessments of the atmospheric
ozone distribution and associated climate change therefore demand accurate
vertically resolved ozone observations with both stratospheric and
tropospheric sensitivity, on both global and regional scales, and both in the
long term and at shorter timescales. Such observations have been acquired by
two series of European nadir-viewing ozone profilers, namely the
scattered-light UV–visible spectrometers of the GOME family, launched
regularly since 1995 (GOME, SCIAMACHY, OMI, GOME-2A/B, TROPOMI, and the
upcoming Sentinel-5 series), and the thermal infrared emission sounders of
the IASI type, launched regularly since 2006 (IASI on Metop platforms and the
upcoming IASI-NG on Metop-SG). In particular, several Level-2 retrieved,
Level-3 monthly gridded, and Level-4 assimilated nadir ozone profile data
products have been improved and harmonized in the context of the ozone
project of the European Space Agency's Climate Change Initiative (ESA
Ozone_cci). To verify their fitness for purpose, these ozone datasets must
undergo a comprehensive quality assessment (QA), including (a) detailed
identification of their geographical, vertical, and temporal domains of
validity; (b)Â quantification of their potential bias, noise, and drift and
their dependences on major influence quantities; and (c)Â assessment of the
mutual consistency of data from different sounders. For this purpose we have
applied to the Ozone_cci Climate Research Data Package (CRDP) released in
2017 the versatile QA and validation system Multi-TASTE, which has been
developed in the context of several heritage projects (ESA's Multi-TASTE,
EUMETSAT's O3M-SAF, and the European Commission's FP6Â GEOmon and FP7Â QA4ECV).
This work, as the second in a series of four Ozone_cci validation papers,
reports for the first time on data content studies, information content
studies and ground-based validation for both the GOME- and IASI-type climate
data records combined. The ground-based reference measurements have been
provided by the Network for the Detection of Atmospheric Composition
Change (NDACC), NASA's Southern Hemisphere Additional Ozonesonde
programme (SHADOZ), and other ozonesonde and lidar stations contributing to
the World Meteorological Organisation's Global Atmosphere Watch (WMO GAW).
The nadir ozone profile CRDP quality assessment reveals that all nadir ozone
profile products under study fulfil the GCOS user requirements in terms of
observation frequency and horizontal and vertical resolution. Yet all
L2Â observations also show sensitivity outliers in the UTLS and are strongly
correlated vertically due to substantial averaging kernel fluctuations that
extend far beyond the kernel's 15 km FWHM. The CRDP typically does not
comply with the GCOS user requirements in terms of total uncertainty and
decadal drift, except for the UV–visible L4 dataset. The drift values of the
L2 GOME and OMI, the L3Â IASI, and the L4Â assimilated products are found to be
overall insignificant, however, and applying appropriate altitude-dependent
bias and drift corrections make the data fit for climate and atmospheric
composition monitoring and modelling purposes. Dependence of the Ozone_cci
data quality on major influence quantities – resulting in data screening
suggestions to users – and perspectives for the Copernicus Sentinel missions
are additionally discussed
Long-term changes in UT/LS ozone between the late 1970s and the 1990s deduced from the GASP and MOZAIC aircraft programs and from ozonesondes
International audienceWe present ozone measurements of the Global Atmospheric Sampling Program (GASP) performed from four commercial and one research aircraft in the late 1970s to compare them with respective measurements of the ongoing MOZAIC project. Multi-annual averages of UT/LS ozone were built using the aircraft data sets (1975-1979 and 1994-2001), and long-term changes between the 1970s and 1990s were derived by comparison. The data were binned relative to the dynamical tropopause to separate between UT and LS air masses. LS data were analysed using equivalent latitudes. In the UT, pronounced increases of 20-40% are found over the Middle East and South Asia in the spring and summer seasons. Increases are also found over Japan, Europe, and the eastern parts of the United States depending on season. LS ozone over northern mid- and high latitudes was found to be lower in the 1990s compared to the 1970s in all seasons of the year. In addition, a comparison with long-term changes deduced from ozonesondes is presented. The early 1970s European Brewer-Mast (BM) sonde data agree with GASP within the range of uncertainty (UT) or measured slightly less ozone (LS). In contrast, the 1990s BM sensors show consistently and significantly higher UT/LS ozone values than MOZAIC. This unequal behaviour of aircraft/sonde comparisons in the 1970s and 1990s leads to differences in the estimated long-term changes over Europe: while the comparison between GASP and MOZAIC indicates ozone changes of −5% to 10% over Europe, the sondes suggest a much larger increase of 10%-35% depending on station and season, although statistical significance is not conclusive due to data sample limitations. In contrast to the BM sondes, the Electrochemical Cell (ECC) sonde at Wallops Island, USA, measured higher UT ozone than both GASP and MOZAIC. Hence, long-term changes from GASP/MOZAIC agree within the range of uncertainty with the changes deduced from Wallops Island
Trajectory matching of ozonesondes and MOZAIC measurements in the UTLS – Part 1: Method description and application at Payerne, Switzerland
International audienceAbstract. With the aim of improving ozonesonde observations in the upper troposphere/lower stratosphere (UTLS), we use three-dimensional forward and backward trajectories, driven by ERA-Interim wind fields to match and compare ozonesonde measurements at Payerne (Switzerland) with observations from the MOZAIC aircraft program from 1994–2009. The uncertainties associated with the sonde–MOZAIC match technique were assessed using "self-matches", i.e. matches of instruments of the same type, such as MOZAIC–MOZAIC. Despite strong vertical gradients of ozone at the tropopause, which render the match approach difficult, the method provides excellent results, showing mean differences between different MOZAIC aircraft of ±2% (typically with a few hours between the up- and downstream match points). Matches between MOZAIC aircraft and Payerne ozonesondes show an agreement of ±5% for sondes equipped with electrochemical concentration cells (ECC) and between < 5% (not scaled to total ozone) and < 10% (scaled) for the Brewer–Mast (BM) sondes after 1998. Prior to 1998, BM sondes show an offset of around 20% (scaled). No break can be identified through the change from the BM to ECC sonde types in September 2002. A comparison of BM sondes with ozone measurements from the NOXAR B747 project for the period 1995–1996 show a smaller offset of around 15% (scaled), which may indicate a small drift in the MOZAIC calibration
Arctic winter 2005: Implications for stratospheric ozone loss and climate change
The Arctic polar vortex exhibited widespread regions of low temperatures during the winter of 2005, resulting in significant ozone depletion by chlorine and bromine species. We show that chemical loss of column ozone (deltaO3) and the volume of Arctic vortex air cold enough to support the existence of polar stratospheric clouds (V_PSC) both exceed levels found for any other Arctic winter during the past 40 years. Cold conditions and ozone loss in the lowermost Arctic stratosphere (e.g., between potential temperatures of 360 to 400 K) were particularly unusual compared to previous years. Measurements indicate DO3 = 121 ± 20 DU and that deltaO3 versus V_PSC lies along an extension of the compact, near linear relation observed for previous Arctic winters. The maximum value of V_PSC during five to ten year intervals exhibits a steady, monotonic increase over the past four decades, indicating that the coldest Arctic winters have become significantly colder, and hence are more conducive to ozone depletion by anthropogenic halogens
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